Low density coring material

ABSTRACT

A low density coring material is described. In one embodiment, the low density coring material consists essentially of: about 40 to about 80 wt % resin; 0 to about 50 wt % monomer; 0 to about 5 wt % dispersion aid; 0 to about 5 wt % accelerator; about 3 to about 7 wt % microspheres; and about 1 to about 5 wt % catalyst; wherein a density of the cured coring material is less than about 5.0 lbs/gal. Composites made using the low density coring material and methods of making composites are also described.

RELATED APPLICATIONS

This application is a divisional application of U.S. Utility patentapplication Ser. No. 12/853,382 filed 10 Aug. 2010; the contents ofwhich are hereby incorporated by reference.

FIELD OF THE INVENTION

This invention relates to a lightweight, polymer based coring materialthat can be used to replace higher density materials in compositemanufacturing.

BACKGROUND OF THE INVENTION

Composite materials such as fiberglass reinforced plastic (FRP) are usedin a variety of applications, including marine, transportation, energy,and construction. As one illustrative example, an FRP composite 10 for amarine application has a structure as illustrated in FIG. 1. There is agelcoat layer 15 followed by 1 layer with 1.0 oz. resin/glass 20. Nextcome 4 layers with 1.5 oz. resin/glass 25. They are followed by 1 layerwith 1.0 oz. resin/glass 30 and a wood, foam, or honeycomb reinforcementlayer 35. This composite contains about 8 oz. of resin/glass, whichgives the composite good strength.

However, it would be desirable to reduce the weight of the composite forsome applications. It would also be desirable to maintain the propertiesat the same level or to only have a slight reduction in properties.

Attempts have been made to utilize alternative materials in FRPcomposites. For example, lightweight materials such as balsa andCOREMAT®. have been tried. However, these materials require much moretime to utilize. In addition, they are more expensive to use because ofthe very high resin demand. Furthermore, they cannot be used in alllaminate structures due to the difficulty of hand laying them in smallradius areas. Other low density materials do not provide sufficientweight reduction.

Therefore, there is a need for a material which allows the weight of acomposite to be reduced.

SUMMARY OF THE INVENTION

The present invention meets this need. One aspect of the invention is alow density coring material. In one embodiment, the low density coringmaterial consists essentially of: about 40 to about 80 wt % resin; 0 toabout 50 wt % monomer; 0 to about 5 wt % dispersion aid; 0 to about 5 wt% accelerator; about 3 to about 7 wt % microspheres; and about 1 toabout 5 wt % catalyst; wherein a density of the cured coring material isless than about 5.0 lbs/gal.

Another aspect of the invention is a composite. In one embodiment, thecomposite includes a first layer of resin/glass; a layer of low densitycoring material adjacent to the first layer of resin/glass, the coringmaterial consisting essentially of: about 40 to about 80 wt % resin; 0to about 50 wt % monomer; 0 to about 5 wt % dispersion aid; 0 to about 5wt % accelerator; about 3 to about 7 wt % microspheres; and about 1 toabout 5 wt % catalyst; wherein a density of the cured coring material isless than about 5.0 lbs/gal; and a second layer of resin/glass or a bulklayer.

Another aspect of the invention is a method of making a composite. Inone embodiment, the method includes depositing a first layer ofresin/glass; at least partially curing the first layer; depositing alayer of low density coring material adjacent to the at least partiallycured first layer, the coring material consisting essentially of: about40 to about 80 wt % resin; 0 to about 50 wt % monomer; 0 to about 5 wt %dispersion aid; 0 to about 5 wt % accelerator; about 3 to about 7 wt %microspheres; and about 1 to about 5 wt % catalyst; at least partiallycuring the layer of coring material; and depositing a second layer ofresin/glass or a bulk layer adjacent to the layer of at least partiallycured coring material.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustration of a prior art composite.

FIG. 2 is an illustration of one embodiment of a composite madeaccording to the present invention.

FIG. 3 is a flow chart showing one embodiment of a method of making thelow density coring material.

FIG. 4 is a flow chart showing one embodiment of a method of making acomposite using the low density coring material.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a very lightweight, polymer basedcoring material that can be used to replace higher density materialsused in composite manufacturing. A composite made using the low densitycoring material can have a density about 10 to about 50% lighter thannormal composite while retaining or improving the physical properties ofnormal composites. It allows reduced cycle time to manufacture thecomposite. It can also reduce the construction needed to produce openmolding laminate structure. The low density coring material can besprayed using available spray equipment, or it can be applied by hand.

The low density coring material has a very low cured density of lessthan about 5.0 lbs/gal, or about 2.8 to about 5.0 lbs/gal, or about 2.8to about 4.5 lbs/gal, or about 2.8 to about 4.0 lbs/gal, or about 2.8 toabout 3.5 lbs/gal. It provides high flexural strength, e.g., theflexural strength can be equal to or higher than a part made withstandard polyester FRP. In some applications, it would be acceptable forthe flexural strength to be slightly less than a part made with standardpolyester FRP. It can improve productivity compared to traditional FRP.It provides high build, for example, there is no sag up to 750 mils inone pass.

FIG. 2 illustrates an example of a composite structure 110 made usingthe low density coring material. There is a gelcoat layer 115 and 1layer with 1.0 oz. resin/glass 120 followed by 1 layer with 1.5 oz.resin/glass 125. This is followed by a layer of the low densitysprayable material 140. This is followed by 1 layer with 1.5 oz.resin/glass 125 and 1 layer with 1.0 oz. resin/glass 130. The wood,foam, or honeycomb reinforcement layer 135 is last.

The low density coring material typically contains: about 40 to about 80wt % resin, or about 65 to about 75 wt %, or about 68 wt %; 0 to about50 wt % monomer, or about 20 to about 25 wt %, or about 24 wt %; 0 toabout 5 wt % dispersion aid, or about 0.5 to about 0.8 wt %, or about0.7 wt %; 0 to about 5 wt % accelerators, or about 0.05 to about 0.1 wt%, or about 0.08 wt %; about 3 to about 7 wt % microspheres; or about3.8 to about 4.8 wt %, or about 4.3 wt %; and about 1 to about 5 wt %catalyst, or about 2.5 to about 3.5 wt %, or about 3.0 wt %.

FIG. 3 illustrates a method of making the low density coring material.One or more resins are provided at block 200. Typically, about 40 toabout 80 wt % of the composition is a polyester resin. Suitable resinscan be obtained from Reichhold Chemical, for example. The monomer (ifused) is provided at block 205. The monomer is typically 0 to about 50wt % of the composition. Suitable monomers include, but are not limitedto, styrene monomers.

A dispersion aid (0-5 wt %) can be added at block 210. The resin,monomer, and dispersion aid are mixed at block 215. The mixer can have alow shear helix blade and a high shear blade, if desired. The componentsmix readily. For example, suitable mixing can be obtained by initiallymixing at low speed (e.g., about 20 rpm) with the helix blade, then athigh speed (e.g., about 1100-1200 rpm) using the high shear blade.

One or more accelerators can be added at block 220. Suitableaccelerators include, but are not limited to, DMPT, DMA, DMAA, cobaltoctoate, potassium octoate, copper napthanate and quaternary ammoniumsalts. The accelerators generally comprise 0 to about 5 wt % of thecomposition. The accelerators are mixed with the resin mixture for about5 minutes with the helix blade at low speed (about 30 rpm) and with thehigh shear blade at high speed (1200-1300 rpm).

The high shear blade is turned off, the helix blade is put at a lowspeed (about 2-3 rpm), and the microspheres are added at block 230. Themicrospheres are included to reduce the density of the material. Glassor plastic microspheres can be used. When the low density coringmaterial is to be applied by spraying, it is desirable to use plasticmicrospheres so that they do not break during the spraying process.

The microspheres are typically present in an amount of about 3 to about7 wt %. If the level is above about 7 wt %, it is difficult to obtain ahomogeneous mixture. When the mixture is sprayed or applied by hand, thelayer has clumps and is not smooth, which affects the integrity andstrength of the layer. If the level is less than about 3 wt %, theweight is not reduced below about 5 lbs/gal, and there is no advantageto the material.

The low density coring material is then mixed with the helix blade(e.g., about 20 rpm) and no shear for 30 min at block 235, and filteredthrough a mesh filter at block 240.

The low density coring material should have a gel time of about 7 toabout 10 min (25.0 g. coring material with 0.75 g. MEKP 925 (1.0%vol/vol), mix for 20 sec). The viscosity should be about 7,000 to about13,000 cps (RVT w/heliopath adapter, T-C @ 20 rpm measured with aBrookfield viscometer), or about 7,000 to about 10,000 cps. Thethixatropic index should be about 1.5-7.0 cps (RVT w/heliopath adapter,T-C @ 2.5/20 rpm) The weight per gallon (WPG) should be less than about5.0 lbs/gal, and the % non-volatiles should be 45.0-55.0.

A composite can be made using the method illustrated in FIG. 4. A layerof resin/glass is deposited at block 300. The layer of resin/glass canbe sprayed on or applied by hand. The glass content of this layer ofresin/glass should be about 30 to about 40%, or about 37%. If the glasscontent is lower than about 30%, the physical properties of thecomposite will be reduced, and the weight/ft.sup.2 will increase andaffect the weight per part savings. If the glass content is above about40%, lower glass shear could result. The minimum final weight of thelayer can be about 1.5 oz, although it could be higher if needed forstrength. The lower the weight of the resin/glass layers, the lower theweight of the overall composite.

The catalyst for the resin/glass layer should be present in an amount ofabout 1% by volume. The catalyst % may vary depending on the temperatureand cure of the resin used.

The first layer should be at least partially cured when the low densitycoring material is applied. It is desirably cured until it is gelledfirm to the point that the first layer does not move and in the tackstage. The low density coring material should be applied prior to thefirst layer reaching a tack-free state to avoid delamination problems.The time to reach the gelled firm/tack stage will vary depending on thetemperature, formulation, and cure of the resin used in the first layer.

The surface of the first layer should be checked at block 305. It shouldbe inspected for air voids, and any dry glass fibers, dust, and otherparticles should be removed.

The layer of low density coring material is applied at block 310. Theviscosity of the low density coring material should be in the range ofabout 7,000 to about 13,000 cps, and the density should be less thanabout 5.0 lbs/gal. The gel time should be about 7 to about 12 min orabout 7 to about 10 min for a 100 g mass. The typical layer thickness ismore than about 60 mils.

The catalyst for the low density coring material is typically MEKP(methyl ethyl ketone peroxide) at a level of about 1.0 to about 5.0 wt%, or about 2.5 to about 3.5 wt %. The catalyst is added in theapplication equipment when spraying, and it is mixed in beforeapplication when being applied by hand.

The low density coring material can be sprayed or applied by hand ifdesired. When spray applied, the thickness of the layer of low densitycoring material should be checked after each pass. The typical (wet)thickness per pass is about 15 to about 40 mils. If the dry thickness of80 to 96 mils is not reached after two passes, a third pass should besprayed, and the thickness checked again. The spraying should becontinued until the desired thickness is obtained.

The low density coring material should be at least partially cured whenthe next layer is applied. It is desirably cured for at least about 20min or more. The surface cure of the low density coring material can bechecked before applying a resin/glass layer. A durometer reading of 35will typically be obtained within about 45 min. (A scale model (307)Type L durometer) at 70° F. and will provide good strength. Thedurometer build will vary with temperatures above or below 70° F. andwith humidity.

The surface of the low density coring material should be checked atblock 315. Any rough spots or lumps should be removed to avoid secondlayer blisters, and any dust or other particles should be removed.

The bulk layer (the support material, e.g., wood, foam, or honeycomb) ora second (or more) resin/glass layer should then be applied at block320. The bulk layer should generally be applied to the low densitycoring material after it has returned to ambient temperature and within3 hrs of application. The characteristics of the additional resin/glasslayer(s) could be similar to those for the first resin/glass layer orthey could be different.

One of skill in the art will recognize that additional layers can beincluded before or after those described above. For example, there canbe a gelcoat, and/or a barrier coat before the first resin/glass layer.There can be one or more resin/glass layers before the low densitycoring material, and one or more resin/glass layers after the lowdensity coring material. There can be a bulk layer after one or moreresin/glass layers or the bulk layer can directly follow the low densitycoring material.

Having described the invention in detail and by reference to specificembodiments thereof, it will be apparent that modifications andvariations are possible without departing from the scope of theinvention defined in the appended claims. More specifically, althoughsome aspects of the present invention are identified herein as preferredor particularly advantageous, it is contemplated that the presentinvention is not necessarily limited to these preferred aspects of theinvention.

What is claimed is:
 1. A process for making a composition for a lowdensity coring material comprising: providing one or more resins, amonomer, and a dispersion aid; performing a first mixing of the one ormore resins, the monomer, and the dispersion aid with a mixer to form aresin mixture; adding one or more accelerators into the resin mixture;performing a second mixing of the added one or more accelerators and theresin mixture; adding microspheres to the mixture of the one or moreaccelerators and the resin mixture while performing a third mixing; andperforming a fourth mixing and filtering the composition through a meshto yield the low density coring material, the coring material having acured state and an uncured state, the viscosity of the coring materialin the uncured state is in a range of from 7,000 to 13,000 cps, whereina density of the cured coring material is less than about 5.0 lbs/gal, alayer of low density coring material having a wet thickness from 15 to40 mils per pass.
 2. The process of claim 1 wherein said one or moreresins are present from 40 to 80 wt % of the composition.
 3. The processof claim 1 wherein said one or more resins is a polyester resin.
 4. Theprocess of claim 1 wherein said monomer is present up to 50 wt % of thecomposition.
 5. The process of claim 1 wherein said monomer is a styrenemonomer.
 6. The process of claim 1 wherein the dispersion aid is presentup to 50 wt % of the composition.
 7. The process of claim 1 wherein thefirst mixing further comprises by initially mixing at low speed of about20 rpm with a helix blade, and then mixing at high speed of 1100-1200revolutions per minute (rpm) using a high shear blade.
 8. The process ofclaim 1 wherein said one or more accelerators comprise at least one ofdimethyl-p-toluidine (DMPT), dimethylaniline (DMA),1,3-dimethylamylamine (DMAA), cobalt octoate, potassium octoate, coppernapthanate and quaternary ammonium salts.
 9. The process of claim 1wherein said one or more accelerators are present up to 5 wt % of thecomposition.
 10. The process of claim 1 wherein the second mixingfurther comprises mixing the accelerators are with the resin mixture forabout 5 minutes with a helix blade at low speed of 30 rpm and with ahigh shear blade at high speed of from 1200 to 1300 rpm.
 11. The processof claim 1 wherein the third mixing further comprises mixing with ahelix blade at a low speed of from 2 to 3 rpm.
 12. The process of claim1 wherein the microspheres are glass or plastic.
 13. The process ofclaim 1 wherein the microspheres are 3 to 7 wt % of the composition. 14.The process of claim 1 wherein the fourth mixing further comprisesmixing with a helix blade at about 20 rpm and no shear for about 30minutes.
 15. The process of claim 1 wherein the density of a layer ofthe cured coring material is in a range of from 2.8 to 4.0 lbs/gal.